1. Field of the Invention.
The invention relates to apparatus and methods associated with color technology and, more particularly, to pattern recognition apparatus and methods for comparing data representative of measured patterns with data representative of reference or predefined patterns.
2. Description of Related Art
It is well known that the term "color" as applied to electromagnetic radiation represents in part the relative energy distribution of radiation within the visible spectrum. That is, light providing a stimulus to the human eye, and having a particular energy distribution, may be perceived as a substantially different color than light of another energy distribution. Concepts relating to the characteristics of color and light waves are the subject of numerous well-known texts, such as Principles of Color Technology, Meyer, Jr. and Saltzman (Wiley 1966) and The Measurement of Appearance, Hunter and Harold (Wiley 2nd Ed. 1987).
In recent years, the capability of maintaining the "quality of color" has been of significant importance in various industries such as, for example, the fields of graphic arts, photography and color film processing. For purposes of performing sample testing and other activities in furtherance of maintaining color quality, it is necessary to first determine an appropriate means for "measuring" and "describing" color. A substantial amount of research has been performed during the past 50 years with respect to appropriate methods and standards for color measurement and description.
For purposes of describing color, and from a purely "physical" point of view, the production of color requires three things: a source of light; an object to be illuminated and a means for perceiving the color of the object. The means for perceiving the color can be the human eye and brain or, alternatively, electrical and electromechanical apparatus such as a photosensitive detector and associated auxiliary devices utilized for detecting light. In general, it is desirable to provide a means for measuring color so as to assess the manner in which an image will appear to a human observer, or the manner in which an image will perform in a photographic or other type of reproduction printing operation.
Although human perception and interpretation of color can be useful, reliance on such perception and interpretation can be highly subjective. That is, human nature may cause one person's perception of the color of a particular object to be substantially different from the perception of another. In addition, eye fatigue, age and other physiological factors can influence color perception. Further, visual human perception is often insufficient for color description. For example, certain object samples may be visually perceived under one light source as substantially "matching", and yet may actually have very different spectral characteristics and may be perceived as "nonmatching" under another light source. In view of the foregoing, it is desirable to employ color measurement and description techniques which are objective in nature, and capable of differentiating among object samples having different color characteristics.
Various devices have been developed and are widely utilized to measure and quantitatively describe color characteristics of object samples. Many of these devices provide measurements related to the spectral characteristics of the samples. Described simplistically, when light is directed onto an object sample to be measured for color, the object may absorb a portion of the light energy, while correspondingly passing through or reflecting (if the object is opaque) other portions of the light. The color characteristics of the object sample will depend in part on the spectral characteristics of the object. That is, the effect of an object on light can be described by its spectral transmittance or reflectance curves (for transparent or opaque materials, respectively). These spectral characteristic curves indicate the fraction of the source light at each wavelength transmitted by or reflected from the materials. Such curves are a means for describing the effect of an object on light in a manner similar to the use of a spectral energy distribution curve for describing the characteristics of a source of light. Instruments utilized for generating such spectral characteristic curves are typically referred to as spectrophotometers.
In accordance with conventional optical physics, it is known that the proportion of light incident to an object sample and absorbed by such a sample is independent of the light intensity. Accordingly, a quantitative indication of the spectral characteristics of an object sample can be defined as the "transmittance" or "reflectance" of the sample. That is, the transmittance of a substantially transparent object can be defined as the ratio of power transmitted over light power incident to the sample. Correspondingly, for an opaque object sample, the reflectance can be defined as the ratio of power reflected from the object over the incident light power.
For collimated light, these ratios can be expressed in terms of intensities, rather than power. Furthermore, because of the nature of transmittance/reflectance and the optical characteristics of the human eye, it is advantageous to express these ratios in logarithmic form. Accordingly, one parameter widely used in the field of color technology for obtaining a quantitative measurement or "figure of merit" is typically characterized as optical "density." The optical density of an object sample is typically defined as follows: EQU Optical Density=D=-log.sub.10 T or -log.sub.10 R (Equation 1)
where T represents transmittance of a transparent object and R represents reflectance of an opaque object. In accordance with the foregoing, if an object sample absorbed 90% of the light incident upon the sample, and the object were opaque, the reflectance would ideally be 10%. The density of such a sample would then be characterized as unity. Correspondingly, if 99.9% of the light were absorbed, the reflectance would be 0.1% and the density would be 3. Similarly, the density of an "ideal" object reflecting 100% of the light incident upon the object would be 0.
To provide a relative measurement of color, it is possible to utilize the principles of optical density, without requiring measurement or knowledge of the absolute values of total incident light intensity or reflectance. That is, for example, it is possible to obtain relative color measurements among a series of object samples by utilizing a particular geometric configuration of light, object sample and reflectance or transmittance detector for each measurement, and standardizing the measurements in some desired manner.
In brief summary, optical density is a measurement of the modulation of light or other radiant flux by an object sample, such as a given area of a photographic print. Density measurements provide a means to assess the manner in which an image will appear to a human observer, or the way an image will perform in a film processing operation. Density measurements can be utilized to produce sensitometric curves to evaluate various printing and reproduction characteristics, as well as utilization to control various photographic operations, such as film processing.
For purposes of measuring optical densities, it is well known to employ a device typically characterized as a "densitometer." These densitometers are often categorized as either "reflection" densitometers, employed for optical density measurements of opaque objects, or are otherwise characterized as "transmittance" densitometers. Transmittance densitometers are employed for determining spectral characteristics of various non-opaque materials.
Densitometers are utilized in various industries for performing a variety of functions. For example, densitometers can be conveniently employed in color film processing applications. Processes associated with these applications will be described in greater detail in subsequent paragraphs herein.
To assist in describing the principles of densitometer apparatus in which concepts of the present invention may be employed, FIG. 1 illustrates a simplified schematic representation of a known reflection densitometer configuration 100. A configuration of this type is described in detail in the commonly assigned and currently pending U.S. Pat. Application Ser. No. 534,205, filed June 7, 1990, which is a continuation of commonly assigned U.S. Patent Application Ser. No. 105,424, filed Oct. 5, 1987 and now abandoned. Densitometer apparatus of the type shown. in FIG. 1 are characterized as reflection densitometers, and utilized to provide color density measurements of opaque materials as previously described.
Referring specifically to FIG. 1, and to numerical references therein, the densitometer apparatus 100 includes a light source unit 102 having a source light 104. With respect to optical density measurements in photography, color film processing, and other industrial fields, various standards have been developed for densitometer light source illuminants. For example, densitometer light source standards have previously been described in terms of a tungsten lamp providing an influx from a lamp operating at a Planckian distribution of 3000.degree. K. Other suggested standards have been developed by the American National Standards Institute ("ANSI") and the International Organization for Standardization ("ISO"). These source light densitometer standards are typically defined in terms of the spectral energy distribution of the illuminant. The source light 104 preferably conforms to an appropriate standard and can, for example, comprise a filament bulb meeting a standard conventionally known in the industry as 2856K ANSI. Power for the source light 104 and other elements of the densitometer apparatus 100 can be provided by means of conventional rechargeable batteries or, alternatively, interconnection to AC utility power.
The source light 104 projects light through a collimating lens 106 which serves to focus the electromagnetic radiation from the source light 104 into a narrow collimated beam of light rays. Various types of conventional and well-known collimating lenses can be employed. The light rays transmitted through the collimating lens 106 project through an aperture 108. The dimensions of the aperture 108 will determine the size of the irradiated area of the object sample under test.
Various standards have been defined for preferable sizes of the irradiated area. Ideally, the aperture 108 is of a size such that the irradiance is uniform over the entire irradiated area. However, in any physically realizable densitometer arrangement, such uniform irradiance cannot be achieved. Current standards suggest that the size of the irradiated area should be such that irradiance measured at any point within the area is at least 90% of the maximum value. In addition, however, aperture size is typically limited to the size of the color bar or color patch area to be measured, and is also sized so as to reduce stray light.
The light rays emerging from the aperture 108 (illustrated as rays 110 in FIG. 1) are projected onto the irradiated area surface of an object sample 112 under test. The sample 112 may be any of numerous types of colored opaque materials. For example, in the printing industry, the sample 112 may be an ink-on-paper sample comprising a portion of a color bar at the edge of a color printing sheet. Further, with respect to the illustrative embodiment of a densitometer apparatus employing the principles of the invention as described in subsequent paragraphs herein, the sample 112 may be a control strip employed in the color film processing industry.
As the light rays 110 are projected onto the object sample 112, electromagnetic radiation shown as light rays 114 will be reflected from the sample 112. Standard detection configurations have been developed, whereby reflected light is detected at a specific angle relative to the illumination light rays 110 projected normal to the plane of the object sample 112. More specifically, standards have been developed for detection of reflected light rays at an angle of 45.degree. to the normal direction of the light rays 110. This angle of 45.degree. has become a standard for reflectance measurements, and is considered desirable in that this configuration will tend to maximize the density range of the measurements. In addition, however, the 45.degree. differential also represents somewhat of a relatively normal viewing configuration of a human observer (i.e. illumination at a 45.degree. angle from the viewer's line of sight).
For purposes of providing light detection, a spectral filter apparatus 116 is provided. The filter apparatus 116 can include a series of filters 118, 120 and 122. The filters 118, 120 and 122 are employed for purposes of discriminating the cyan, magenta and yellow spectral responses, respectively. That is, each of the filters will tend to absorb light energy at frequencies outside of the bandwidth representative of the particular color hue of the filter. For example, the cyan filter 118 will tend to absorb all light rays, except for those within the spectral bandwidth corresponding to a red hue. By detecting reflected light rays only within a particular color hue bandwidth, and obtaining an optical density measurement with respect to the same, a "figure of merit" can be obtained with respect to the quality of the object sample coloring associated with that particular color hue.
It is apparent from the foregoing that the actual quantitative measurement of color density or color reflectance is dependent in substantial part on the spectral transmittance characteristics of the filters. Accordingly, various well-known standards have been developed with respect to spectral characteristics of densitometer filters. For example, one standard for densitometer filters is known as the ANSI status T color response. The spectral response characteristics of filters meeting this standard are relatively wide band (in the range of 50-60 namometers bandwidth) for each of the cyan, magenta and yellow color hues. Other spectral response characteristic standards include, for example, what is known as G-response, which is somewhat similar to status T, but is somewhat more sensitive with respect to yellow hues. An E-response represents a European response standard.
Although the filters 118, 120 and 122 are illustrated in the embodiment shown in FIG. 1 as the cyan, magenta and yellow color shades, other color shades can clearly be employed. These particular shades are considered somewhat preferable in view of their relative permanence, and because they comprise the preferred shades for use in reflection densitometer calibration. However, it is apparent that different shades of red, blue and yellow, as well as entirely different colors, can be utilized with the densitometer apparatus 100.
The spectral filters 118, 120 and 122 may not only comprise various shades of color, but can also be one of a number of several specific types of spectral response filters. For example, the filters can comprise a series of conventional Wratten gelatin filters and infrared glass. However, various other types of filter arrangements can also be employed.
The spectral filters 118, 120 and 122 are preferably positioned at a 45.degree. angle relative to the normal direction from the plane of the object sample 112 under test. In the particular example shown in FIG. 1, each of these filters is maintained stationary and utilized to simultaneously receive light rays reflected from the object sample 112. Further, although the particular example illustrated in FIG. 1 may include a stationary object sample 112, the example embodiment of a densitometer apparatus employing principles of the invention as described in subsequent paragraphs herein can include an object sample which is continuously moving relative to the spectral filter arrangement. In such an instance, the actual spectral filter measurements may be obtained simultaneously or, alternatively, in sequence.
As further shown in FIG. 1, the portion of the reflected light rays 114 passing through the filters 118, 120 and 122 (shown as light rays 124, 126 and 128, respectively) impinge on receptor surfaces of photovoltaic sensor cells. The sensor cells are illustrated in FIG. 1 as sensors 132, 134 and 136 associated with the spectral filters 124, 126 and 128, respectively. The sensors 132, 134 and 136 can comprise conventional photoelectric elements adapted to detect light rays emanating through the corresponding spectral filters. The sensors are further adapted to generate electrical currents having magnitudes proportional to the intensities of the sensed light rays. As illustrated in FIG. 1, electrical current generated by the cyan sensor 132 in response to the detection of light rays projecting through the filter 118 is generated on line pair 138. Correspondingly, electrical current generated by the magenta sensor 134 is applied to the line pair 140, while the electrical current generated by the yellow sensor 136 is applied as output current on line pair 142. Photoelectric elements suitable for use as sensors 136, 138 and 140 are well-known in the art, and various types of commercially-available sensors can be employed.
The magnitude of the electrical current on each of the respective line pairs will be proportional to the intensity of the reflected light rays which are transmitted through the corresponding spectral filter. These light rays will have a spectral distribution corresponding in part to the product of the spectral reflectance curve of the object sample 112, and the spectral response curve of the corresponding filter. Accordingly, for a particular color shade represented by the spectral response curve of the filter, the magnitude of the electrical current represents a quantitative measurement of the proportional reflectance of the object sample 112 within the frequency spectrum of the color shade.
As further shown in FIG. 1, the sensor current output on each of the line pairs 138, 140 and 142 can be applied as an input signal to one of three conventional amplifiers 144, 146 and 148. The amplifier 144 is responsive to the current output of cyan sensor 132 on line pair 138, while amplifier 146 is responsive to the sensor current output from magenta sensor 134 on line pair 144. Correspondingly, the amplifier 148 is responsive to the sensor current output from yellow sensor 136 on line pair 142. Each of the amplifiers 144, 146 and 148 provides a means for converting low level output current from the respective sensors on the corresponding line pairs to voltage level signals on conductors 150, 152 and 154, respectively. The voltage levels of the signals on their respective conductors are of a magnitude suitable for subsequent analog-to-digital (A/D) conversion functions. Such amplifiers are well known in the circuit design art, and are commercially available with an appropriate volts per ampere conversion ratio, bandwidth and output voltage range. The magnitudes of the output voltages on lines 150, 152 and 154 again represent the intensities of reflected light rays transmitted through the corresponding spectral filters.
Each of the voltage signal outputs from the amplifiers can be applied as an input signal to a conventional multiplexer 156. The multiplexer 156 operates so as to time multiplex the output signals from each of the amplifiers 144, 146 and 148 onto the conductive path 158. Timing for operation of the multiplexer 156 can be provided by means of clock signals from master clock 160 on conductive path 162. During an actual density measurement of an object sample, the densitometer 100 will utilize a segment of the resultant multiplexed signal which sequentially represents a voltage output signal from each of the amplifiers 144, 146 and 148.
The resultant multiplexed signal generated on the conductive path 158 is applied as an input signal to a conventional A/D converter 164. The A/D converter 164 comprises a means for converting the analog multiplexed signal on conductor 158 to a digital signal for purposes of subsequent processing by central processing unit (CPU) 166. The A/D converter 164 is preferably controlled by means of clock pulses applied on conductor 168 from the master clock 160. The clock pulses operate as "start" pulses for performance of the A/D conversion. The A/D converter 164 can be any suitable analog-to-digital circuit well known in the art and can, for example, comprise 16 binary information bits, thereby providing a resolution of 65K levels per input signal.
The digital output signal from the A/D converter 164 can be applied as a parallel set of binary information bits on conductive paths 170 to the CPU 166. The CPU 166 can provide several functions associated with operation of the densitometer apparatus 100. In the embodiment described herein, the CPU 166 can be utilized to perform these functions by means of digital processing and computer programs. In addition, the CPU 166 can be under control of clock pulses generated from the master clock 160 on path 172. However, a number of the functional operations of CPU 166 could also be provided by means of discrete hardware components.
In part, the CPU 166 can be utilized to process information contained in the digital signals from the conductive paths 170. Certain of this processed information can be generated as output signals on conductive path 176 and applied as input signals to a conventional display circuit 178. The display circuit 178 provides a means for visual display of information to the user, and can be in the form of any one of several well-known and commercially-available display units.
In addition to the CPU 166 receiving digital information signals from the conductive paths 170, information signals can also be manually input and applied to the CPU 166 by means of a manually-accessible keyboard circuit 180. The user can supply "adjustments" to color responses by means of entering information through the keyboard 180. Signals representative of the manual input from the keyboard 180 are applied as digital information signals to the CPU 166 by means of conductive path 182.
The previously described concepts of densitometry can be of primary significance in fields such as the color photography and processing industry. For purposes of illustration and example, the color photograph processing procedure can be described as comprising a series of three process steps. First, the exposed roll or strip of color film is subjected to a process for producing a series of "negatives"' from the exposed film roll or strip. This process is well known in the photography industry and can essentially be characterized as a chemical process for producing a series of negative images, in which the "brightness" values of the photograph subject are reproduced so that the lightest areas are shown as the darkest areas.
Secondly, the color photography development process comprises a step wherein the photographic negative is utilized with photographic paper in a manner such that the photographic paper is subjected to exposure from the negative. In this process, the film base and exposure times can be varied as appropriate to achieve the proper color balance on the exposed paper. Finally, the exposed film paper is subjected to a chemical process for generating the finished photographic prints.
Each of the aforedescribed processes is relatively conventional and well known in the photographic industry. However, each of these processes requires the "setting" of various control variables on the equipment utilized to perform the processes. For example, the processes associated with producing the negatives and processing the exposed paper comprise chemical processes whereby color chemistry variables may be adjusted so as to produce negatives and finished prints of appropriate colors. Correspondingly, the process step whereby the photographic print paper is exposed from the negatives will also have various variables associated with the process. For example, this particular process will involve the use of "white" light sources and spectral filters for exposing the negative onto the photographic paper in differing manners. Further, a variable associated with this particular process comprises the exposure times for the exposure of the negative onto the photographic paper. As an example, the negative may be exposed onto the paper through an unfiltered white light source for a certain predetermined period of time. However, if such an exposure is not producing an appropriate color balance, filters may be employed whereby only a particular color (i.e. energy from a portion of the color spectrum) of the white light source is exposed onto the photographic paper for some portion of the entirety of the exposure time. This type of operation is typically referred to as a "balancing" of the color.
With respect to the final step of the photographic development process, i.e. the processing of the exposed photographic paper to produce the final photographic prints, a number of variables are also associated with this type of process. For example, the chemistry of the film bath may be varied through the use of various chemical mixtures so to again achieve correct print processing to maintain appropriate photograph colors.
Various methods and equipment have been developed for providing the photograph developers with a means for measuring the "quality" of the individual process steps associated with the entirety of the photograph development process. In particular, it is relatively well known to utilize densitometers to measure optical transmittance density of processed negatives and optical reflectance density of processed photographic paper to determine if the equipment is producing appropriate color balances. However, when measuring color densities to determine the quality of the film processing, it is desirable to compare such density measurements against "ideal" processed materials. Accordingly, the field of film processing readily lends itself to the comparison of color densities of materials processed by the operator's own equipment against reference standards.
Further, however, the photographic industry does not have any ideal standards related to each of the process steps associated with film development. Additionally, optimum color densities of processed materials may vary dependent upon the particular type of film or paper material being utilized by the operator. Accordingly, manufactures of film processing equipment and materials will provide their own individual reference standards for purposes of optimizing the film development process.
More specifically, it is known in the field of color photograph film processing to utilize "strips" of negative and paper materials to periodically test the quality of the operator's own processing equipment. In addition, manufacturers also provide "reference" strips of materials which can be characterized as processed strips comprising "ideal" processing of the manufacturers' materials.
To further illustrate the use of the reference strips and the control strips, a strip commonly identified as the Kodak C-41 strip is illustrated in FIG. 2. The C-41 strip is manufactured by Eastman Kodak Company. The strip illustrated in FIG. 2 is identified as strip 200 and comprises a film negative having various color hues associated with the negative. When the film development equipment operator is utilizing film negatives manufactured by Eastman Kodak, the operator will obtain a referenced film strip and a series of control strips having a configuration as shown in FIG. 2. The reference strip can be characterized as a negative which has been fully processed by the manufacturer. The negative is considered to comprise a series of color patches having the "ideal" color hues for the negative processing. Correspondingly, the control strips provided by the manufacturer will be a series of unprocessed strip negatives. The principal use and concept associated with these strips is to allow the operator to adjust the film negative processor so that the color densities of control strips processed by the negative processor will optimally "match" color densities of the reference strip.
To perform the operation of measuring the quality of the negative processing, a densitometer can first be used to measure the transmission densities of the reference strip. Again, these transmission densities represent ideal densities to be achieved by the equipment negative processor. Although it would be possible to utilize color density values somehow identified on the reference strip, such values may not comprise the same density values which will be measured by the operator's own densitometer. That is, the "absolute values" of the color densities are not particularly important. Instead, the quality of the film negative processing by the operator's equipment will be indicated by the comparison of the measured color densities of a processed control strip relative to the measured color densities of the reference strip. Because densitometers may vary in their measurement readings from one device to another, it is of primary importance that the color densities for the reference strip and the control strips be measured by the same device.
After measurement of the color densities associated with the reference strip, a control strip having a similar configuration to the strip 200 is processed by the operator, using the operator's own equipment. Following processing of the film negative, the processed control strip is now measured to determine the color densities associated therewith. The differences in the relative color density measurement values between the reference strip and the processed control strip will indicate to the operator whether any adjustments in the film negative processing operation are required. Indeed, many of the primary manufacturers will provide written "trouble shooting" manuals indicating the types of adjustments which may be necessary in view of certain types of differences between the density measurements associated with the processed control strip and the density measurements associated with the reference strip. As an example, the operator may find that the "green" density value for the processed control strips is continuously lower than the green density value for the reference strip. The written trouble shooting manuals may then provide suggestions as to the particular activities which may be undertaken by the operator with respect to adjustment of the negative processor equipment.
With respect to adjustments to the processing equipment associated with the exposure of the negative onto the photographic paper, manufacturers provide reference and control strips commonly known as "print balance" strips. Such a print balance control strip is illustrated in FIG. 3 as print balance strip 202. As shown in FIG. 3, the strip comprises three color patches identified as the "over", "normal" and "under" patches. These patches comprise color densities which may be expected with respect to photographic paper that has been overexposed, normal and underexposed, respectively. The print balance control strips are employed to maintain a printing balance during the exposure of a negative onto the photographic paper. Again, in a manner similar to the processing step associated with processing the negative, the manufacturers will provide a print balance reference strip, in addition to a series of unprocessed print balance strips. The operator would again measure the color densities of the patches of the reference strip representative of overexposure, normal processing and underexposure. These color density values would then be compared against the actual color density values of materials processed by the operator's own equipment. These measurements can assist the operator in adjusting exposure times and filtering so as to achieve a proper color balance in exposing the negative onto the photographic paper.
With respect to the third step of the overall development process, i.e. the processing of the exposed photographic paper to obtain the final photographic prints, the manufacturers provide further reference and control strips to adjust variables in the processing step. A control strip commonly identified as the Kodak EP-2 strip (manufactured by the Eastman Kodak Company) is illustrated as control strip 204 in FIG. 4. Again, the operator would be provided with the reference strip having the "ideal" color densities. That is, the reference strip would comprise a strips of photographic print having the ideal color densities for this processing step. The operator would measure these reflection color densities and compare the densities against control strips processed by the operator's own equipment. Manufacturers provide written trouble shooting manuals for this processing step in a manner similar to the materials provided for the production of the film negatives. That is, differences in the measured color densities will typically indicate certain problems associated with this step of the film processing. As an example, a relatively substantial distinction in the color densities of particular color patches between a processed control strip and the reference strip may indicate that the bath temperature for the processing of the final photographic print is not appropriate.
The common use of control strips as previously described herein with respect to photographic processing raises several issues. For example, it can be noted that the entirety of the processes described above involves some measurement of optical transmission densities (for the negative) and optical reflection densities (for the film paper). In addition, it is apparent that the measurement of the color densities of the reference strip and the control strips can involve a substantial amount of manual manipulation. Accordingly, it is clearly advantageous to employ a densitometer having the combined functions of reflection density measurement and transmission density measurement. In addition, it is also advantageous to provide a means for "automating" the density measurement functions, dependent upon the particular types of standardized reference and control strips being employed. For purposes of the description of the illustrative embodiment of the invention as subsequently disclosed herein, references to control strips will refer to both reference strips and control strips.
Another problem associated with the use of control strips is the requirement to essentially compare the color densities of patches on the control strips to expected color densities for the particular strips. That is, it is necessary to determine whether the color density "patterns" of the control strips fall within certain tolerances with regard to parameters such as patch size, predominant color, density and the like.
If only one type of control strip were to be utilized with a particular densitometer arrangement, this "pattern recognition" requirement would not present any substantial difficulties. That is, appropriate software for use with the central processing unit of the densitometer could be written for purposes of deriving the specific pattern recognition arrangement required for the specific control strip. However, if the densitometer is to utilize a variety of control strips, it would be somewhat difficult and complex to require the writing of different software packages for different strips. Further, certain control strips have multiple patterns. Accordingly, such patterns can actually be read erroneously in several different ways.
In addition, a substantial advance has been achieved in the art of densitometer development with an automated strip reader densitometer. This automated strip reader densitometer is disclosed in the commonly assigned U.S. Patent Application Ser. No. 309,342 filed Feb. 10, 1989 and referred to herein as the Cargill et al application. The disclosure of the Cargill et al application is hereby incorporated by reference herein. With the automated strip reader densitometer, control strips are essentially read "on the fly" as the control strips pass through various elements of the densitometer. With this type of arrangement, it is essentially necessary to provide a pattern recognition arrangement within the central processing unit which will have the capability of providing an indication as to a match or mismatch of the control strip with previously stored data as the control strip continuously moves through the densitometer.